DihexagonaL Alternating Type. 205 



Large well-defined etchings were obtained upon the 

 unit prism after immersion of 10 seconds in warm 10 

 percent HC1 (see fig. 1). The figures are bounded by four 

 faces, two lateral, one large basal plane, and a small face 

 at one end. The figures are quite unique in form, differ- 

 ing more or less in the primitive and ultimate stages. In 

 the primitive stage the figures appear as relatively deep 

 pits, from which there extend, above or below as the case 

 may be, but always in the same direction on the same 

 face, a face parallel to c ever widening as it extends far- 

 ther and farther from the pit, and at the same time grad- 

 ually approaching the surface, its intersection with which 

 is barely discernible, and in some cases cannot be seen 

 at all. This face finally becomes the base and the most 

 prominent plane of the mature figure. It is readily rec- 

 ognized as a triangular form lying in the scalenohedron 

 zone and resembling a face of that form. The intersec- 

 tions of this face and the lateral faces of the figure can 

 be easily distinguished under the microscope, conse- 

 quently the angle at the apex of this basal plane was 

 measured on several figures, large and small, the readings 

 averaging to 25° 35'. These measurements were very 

 suggestive, as the average reading seemed to correspond 

 with the facial angle at the apex of the scalenohe- 

 dron v (2131) which form occurs on the crystal etched. 

 Repeated measurements of the facial angle proved this to 

 be a fact, and that the two readings are almost identical, 

 the face being 26° and the figures 25° 35', indicating that 

 the face of the figures is parallel to the actual scalenohe- 

 dron occurring on the crystal. The two converging edges 

 of these basal planes meet the edge 1010/2131 at approxi- 

 mately 45° which corresponds to the angle produced by 

 the convergence of the two adjacent edges 1010/2131, 

 placing the lateral bounding planes of the figure in the 

 1010/2131 zone. The plane bounding the smaller end of 

 the figure appeared to be slightly rhomb-shaped, with the 

 large angles turned down to meet the apex of the base. 

 The center of this end face seems to contain a faint 

 groove extending downward, which becomes invisible 

 before it reaches the bottom. Thus the figure in general 

 is much deeper at the narrow end, and is symmetrical 

 with regard to a vertical plane. Figures on adjacent 

 faces are inverted with respect to one another thus 

 revealing the alternating axis of symmetry. 



